The present invention relates to a display device for displaying an image with luminance corresponding to a video signal inputted from the exterior and a luminance control method therefor.
Plasma display devices using PDPs (Plasma Display Panels) have the advantage that thinning and larger screens are possible. In the plasma display devices, images are displayed by utilizing light emission in cases where discharge cells composing pixels are discharged. As light is thus emitted, heat is generated on a glass surface composing the PDP, so that the higher the luminance of an image becomes, the larger the amount of heat generation becomes. Therefore, the temperature of the glass surface is raised. In the worst case, the glass surface is damaged.
In order to solve the above-mentioned problem, an example of a conventional display device is a display device disclosed in JP-A-11-194745. In the display device, the whole surface of a display screen is divided into a plurality of blocks, temperature estimated values are calculated with respect to all the blocks, and the maximum value of the calculated estimated temperatures is compared with a reference temperature to produce a luminance correction coefficient. The luminance of the display screen is controlled by the luminance correction coefficient.
A display on which an image is displayed is generally fixed in its outer periphery. Damage to the display caused by the rise in the temperature with the increase in the luminance may occur in the vicinity of the outer periphery of the display in most cases. That is, the damage to the display depends on the temperature difference rather than the maximum temperature. Generally, the temperature difference between the outer periphery of the display where no heat is generated and the outer periphery of the display screen of the display where heat is generated is the largest. The display may be damaged by thermal stress created by the temperature difference in many cases.
In the conventional display device, however, only when the maximum value of the estimated temperatures reaches not less than the reference temperature, that is, when the temperature of any portion on the display screen exceeds its certain upper-limit value, the luminance is controlled. Therefore, the luminance cannot be always controlled when excessive thermal stress is exerted on the outer periphery, which is most easily damaged, of the display, thereby making it impossible to reliably prevent the display from being damaged.
In the conventional display device, the whole of the display screen is divided into a plurality of blocks, and the estimated temperatures are calculated with respect to all the blocks. Accordingly, operation processing becomes complicated, and long time is required to perform the operation processing. Particularly in recent years, it has been desired to make a display image highly precise. The number of pixels composing the display screen, that is, the number of discharge cells has tended to be increased. In this case, the above-mentioned operation processing has increasingly become complicated, and the processing time is lengthened.
An object of the present invention is to provide a display device capable of more reliably preventing a display from being damaged and a luminance control method therefor.
Another object of the present invention is to provide a display device capable of more reliably preventing a display from being damaged in a small amount of operation and a luminance control method therefor.
A display device according to an aspect of the present invention comprises a display for displaying an image with luminance corresponding to a video signal inputted from the exterior; a temperature estimation circuit for estimating from the video signal a temperature estimated value corresponding to the temperature of a display screen of the display; an operation circuit for finding a temperature difference estimated value using a reference value corresponding to the temperature of the outer periphery of the display and the temperature estimated value; and a control circuit for controlling the luminance of the image displayed on the display on the basis of the temperature difference estimated value.
In the display device, the temperature estimated value corresponding to the temperature of the display screen of the display is estimated from the video signal, and the temperature difference estimated value is found using the temperature estimated value and the reference value corresponding to the temperature of the outer periphery of the display, to control the luminance of the image displayed on the display on the basis of the temperature difference estimated value. Generally, the display on which the image is displayed is fixed in its outer periphery. Accordingly, damage to the display caused by the rise in the temperature with the increase in the luminance may occur in the vicinity of the outer periphery of the display in most cases. Therefore, the luminance is controlled depending on the temperature difference estimated value found from the temperature estimated value corresponding to the temperature of the display screen and the temperature of the outer periphery of the display, as described above, so that the luminance can be controlled on the basis of the temperature difference between the outer periphery of the display which most greatly affects the damage to the display and the display screen, thereby making it possible to more reliably prevent the display from being damaged.
It is preferable that the temperature estimation circuit estimates the temperature estimated value corresponding to the temperature of the outer periphery of the display screen of the display.
In this case, the temperature difference estimated value corresponding to the temperature of the outer periphery of the display screen of the display is estimated from the video signal, and the temperature difference estimated value is found using the temperature estimated value and the reference value corresponding to the temperature of the outer periphery of the display, to control the luminance of the image displayed on the display on the basis of the temperature difference estimated value. The temperature difference estimated value is found from the temperature estimated value corresponding to the temperature of the outer periphery of the display screen and the reference value corresponding to the temperature of the outer periphery of the display. Accordingly, the luminance can be controlled on the basis of the temperature difference between the outer periphery of the display which greatly affects the damage to the display and the outer periphery of the display screen closest to the outer periphery, thereby making it possible to more reliably prevent the display from being damaged. Further, the temperature estimated value operated in order to find the temperature difference estimated value is limited to the temperature estimated value for the outer periphery of the display screen of the display. Accordingly, the amount of operation is made smaller than that in a case where the temperature estimated value on the whole of the display screen, so that the processing is simplified, and the processing time is shortened. As a result, it is possible to more reliably prevent the display from being damaged in a small amount of operation.
It is preferable that the display comprises first and second boards between which a plurality of light emitting elements are formed and to which its outer periphery is fixed, and the outer periphery of the display includes a portion between the light emitting element positioned in the outermost periphery out of the plurality of light emitting elements and a fixed portion of the first and second boards.
In this case, the reference value corresponds to the temperature of the portion between the light emitting element positioned in the outermost periphery and the fixing portion of the first and second boards. Accordingly, the luminance can be controlled using as a basis the temperature of the portion most easily damaged, thereby making it possible to more reliably prevent the display from being damaged.
It is preferable that the temperature estimation circuit estimates the temperature estimated value by integrating data relating to the luminance from the video signal and subtracting the amount of dissipated heat therefrom, and the operation circuit subtracts the reference value from the temperature estimated value, to find the temperature difference estimated value.
In this case, the data relating to the luminance is integrated from the video signal, and the amount of dissipated heat is subtracted therefrom, thereby making it possible to find the temperature estimated value corresponding to the truer temperature. Consequently, the luminance is controlled on the basis of the temperature difference estimated value obtained by subtracting the reference value from the temperature estimated value. Accordingly, it is possible to control the luminance with higher precision to more reliably prevent the display from being damaged.
It is preferable that the control circuit lowers the luminance of the image displayed on the display with the increase in the temperature difference estimated value.
In this case, the luminance is lowered with the increase in the temperature difference estimated value, thereby making it possible to more reliably prevent the display from being damaged.
It is preferable that the control circuit lowers the maximum luminance of the image displayed on the display with the increase in the temperature difference estimated value.
In this case, the maximum luminance is lowered with the increase in the temperature difference estimated value, thereby making it possible to more reliably prevent the display from being damaged as well as making it possible to display, when the luminance other than the maximum luminance is displayed as it is, a good image corresponding to the luminance of the video signal itself.
It is preferable that the display displays the image with a gray scale corresponding to the video signal out of a plurality of gray scales, and the control circuit lowers the luminance of the image displayed on the display at the same ratio for each of the gray scales.
In this case, the luminance is lowered at the same ratio for each gray scale, thereby making it possible to lower the luminance of the display without giving a visually uncomfortable feeling to a viewer.
It is preferable that the display displays the image with a gray scale corresponding to the video signal using a plurality of light emitting formats which are the same in the total number of gray scales and differ in the number of light emitting pulses on each of the gray scales, and the control circuit controls the luminance of the image displayed on the display using the light emitting format selected depending on the temperature difference estimated value out of the plurality of light emitting formats.
In this case, the luminance can be controlled by switching the plurality of light emitting formats in the order of their decreasing numbers of light emitting pulses on the same gray scale with the increase in the temperature difference estimated value, thereby making it possible to lower the luminance without greatly changing the total number of gray scales.
It is preferable that the control circuit divides the display screen of the display into a plurality of blocks, extracts from the plurality of blocks the peripheral block adjacent to the outer periphery of the display screen, and lowers the luminance of the peripheral block.
In this case, the luminance of the peripheral block adjacent to the outer periphery of the display screen is lowered. Accordingly, the image in the block inside the display screen can be displayed with the luminance of the video signal itself, thereby making it possible to provide a display screen having no visually uncomfortable feeling by the viewer as well as to more reliably prevent the outer periphery of the display from being damaged.
It is preferable that the control circuit divides a display screen of the display into a plurality of blocks, extracts from the plurality of blocks the peripheral block adjacent to the outer periphery of the display screen, and makes the luminance of the peripheral block lower than that of the block inside the display screen of the display.
In this case, the luminance of the peripheral block is made lower than that of the block inside the display screen. Accordingly, the luminance of the display screen is smoothly changed, thereby making it possible to provide a display screen having no visually uncomfortable feeling by the viewer as well as to more reliably prevent the outer periphery of the display from being damaged.
It is preferable that the display device further comprises a block extraction circuit for dividing the display screen of the display into a plurality of blocks and extracting from the plurality of blocks the peripheral blocks adjacent to the outer periphery of the display screen, the temperature estimation circuit estimates the temperature estimated values for the peripheral blocks, the operation circuit finds a peripheral block temperature difference estimated value from the temperature estimated values estimated for the peripheral blocks, and the control circuit controls the luminance for each of the peripheral blocks on the basis of the peripheral block temperature difference estimated value.
In this case, the display screen is divided into the plurality of blocks, and the luminance is controlled for each of the peripheral blocks adjacent to the outer periphery of the display screen. Accordingly, the luminance can be controlled more finely, thereby making it possible to provide a display screen having no visually uncomfortable feeling by the viewer as well as to more reliably prevent the outer periphery of the display from being damaged.
It is preferable that the control circuit controls the luminance for each of the peripheral blocks such that the amount of controlled luminance between the adjacent peripheral blocks is smoothly changed on the basis of the peripheral block temperature difference estimated value.
In this case, the amount of controlled luminance between the adjacent peripheral blocks is smoothly changed. Accordingly, a display screen having no visually uncomfortable feeling can be provided for the viewer, and thermal stress created in the outer periphery of the display is smoothly changed, thereby making it possible to more reliably prevent the display from being damaged.
It is preferable that the display device further comprises a block extraction circuit for dividing the display screen of the display into a plurality of blocks and extracting from the plurality of blocks the peripheral blocks adjacent to the outer periphery of the display screen, the temperature estimation circuit estimates the temperature estimated values for the peripheral blocks, the operation circuit finds, out of the temperature estimated values estimated for the peripheral blocks, peripheral block temperature difference estimated values for the peripheral blocks, and extracts from the peripheral block temperature difference estimated values the maximum peripheral block temperature difference estimated value, and the control circuit controls the luminance of the image displayed on the display on the basis of the maximum peripheral block temperature difference estimated value.
In this case, the luminance is controlled using the maximum peripheral block temperature difference estimated value representing the largest temperature difference in the peripheral blocks, thereby making it possible to more reliably prevent the display from being damaged. Further, the luminance is controlled by the maximum peripheral block temperature difference estimated value, thereby simplifying processing for controlling the luminance.
It is preferable that the reference value includes a plurality of reference values which differ depending on the position of the outer periphery of the display.
In this case, the luminance of the image displayed on the display can be controlled using the plurality of reference values which differ depending on the position of the outer periphery of the display. Accordingly, a high reference value is set in a portion where the temperature is easily raised, while a low reference value is set in a portion where the temperature is not easily raised, thereby making it possible to control the luminance on the basis of each of the reference values. As a result, the display can be more reliably prevented from being damaged, and the luminance is not lowered any more than necessary.
It is preferable that the display device further comprises a measurement circuit for measuring the temperature of the outer periphery of the display and outputting to the operation circuit the reference value corresponding to the measured temperature.
In this case, the temperature of the outer periphery of the display is directly measured, thereby making it possible to control the luminance on the basis of the reference value corresponding to the temperature. Even when the reference value is changed by the variation in outside air temperature, for example, it is possible to reliably prevent the display from being damaged.
A luminance control method for a display device according to another aspect of the present invention is a luminance control method for a display device comprising a display for displaying an image with luminance corresponding to a video signal inputted from the exterior, characterized by comprising the steps of estimating from the video signal a temperature estimated value corresponding to the temperature of a display screen of the display; finding a temperature difference estimated value using a reference value corresponding to the temperature of the outer periphery of the display and the temperature estimated value; and controlling the luminance of the image displayed on the display on the basis of the temperature difference estimated value.
In the luminance control method for the display device, the temperature estimated value corresponding to the temperature of the display screen of the display is estimated from the video signal, and the temperature difference estimated value is found using the temperature estimated value and the reference value corresponding to the temperature of the outer periphery of the display, to control the luminance of the image displayed on the display on the basis of the temperature difference estimated value. Generally, the display on which the image is displayed is fixed in its outer periphery. The damage to the display caused by the increase in the luminance may occur in the vicinity of the outer periphery of the display in most cases. Consequently, the luminance is controlled depending on the temperature difference estimated value found from the temperature estimated value corresponding to the temperature of the display screen and the reference value corresponding to the temperature of the outer periphery of the display, thereby making it possible to control the luminance on the basis of the temperature difference between the outer periphery of the display which most greatly affects the damage to the display and the display screen and to more reliably prevent the display from being damaged.
It is preferable that the temperature estimating step comprises the step of estimating the temperature estimated value corresponding to the temperature of the outer periphery of the display screen of the display.
In this case, the temperature estimated value corresponding to the temperature of the outer periphery of the display screen of the display is estimated from the video signal, and the temperature difference estimated value is found using the temperature estimated value and the reference value corresponding to the temperature of the outer periphery of the display, to control the luminance of the image displayed on the display on the basis of the temperature difference estimated value. The temperature difference estimated value is found from the temperature estimated value corresponding to the temperature of the outer periphery of the display screen and the reference value corresponding to the temperature of the outer periphery of the display. Accordingly, the luminance can be controlled on the basis of the temperature difference between the outer periphery of the display which most greatly affects the damage to the display and the outer periphery of the display screen closest to the outer periphery of the display, thereby making it possible to more reliably prevent the display from being damaged. Further, the temperature estimated value operated in order to find the temperature difference estimated value is limited to the temperature estimated value for the outer periphery of the display screen of the display. Accordingly, the amount of operation is made smaller than that in a case where the temperature estimated value on the whole of the display screen is operated, so that the processing is simplified, and the processing time is shortened. As a result, it is possible to more reliably prevent the display from being damaged in a small amount of operation.
It is preferable that the display displays the image on a gray scale corresponding to the video signal using a plurality of light emitting formats which are the same in the total number of gray scales and differ in the number of light emitting pulses on each of the gray scales, and the controlling step comprises the step of controlling the luminance of the image displayed on the display using the light emitting format selected depending on the temperature difference estimated value out of the plurality of light emitting formats.
In this case, the luminance can be controlled by switching the plurality of light emitting formats in the order of their decreasing numbers of light emitting pulses on the same gray scale with the increase in the temperature difference estimated value, thereby making it possible to lower the luminance without greatly changing the total number of gray scales.
It is preferable that the controlling step comprises the step of dividing the display screen of the display into a plurality of blocks, extracting from the plurality of blocks the peripheral blocks adjacent to the outer periphery of the display screen, and lowering the luminance of the peripheral blocks.
In this case, the luminance of the peripheral blocks adjacent to the outer periphery of the display screen is lowered. Accordingly, the image in the block inside the display screen can be displayed with the luminance of the video signal itself, thereby making it possible to provide a display screen having no visually uncomfortable feeling by the viewer as well as to more reliably prevent the outer periphery of the display from being damaged.
It is preferable that the luminance control method for the display device further comprises the step of dividing the display screen of the display into a plurality of blocks and extracting from the plurality of blocks the peripheral blocks adjacent to the outer periphery of the display screen, the temperature estimating step comprises the step of estimating the temperature estimated values for the peripheral blocks, the temperature difference estimated value operating step comprises the step of finding a peripheral block temperature difference estimated value from the temperature estimated values estimated for the peripheral blocks, and the controlling step comprises the step of controlling the luminance for each of the peripheral blocks on the basis of the peripheral block temperature difference estimated value.
In this case, the display screen is divided into the plurality of blocks, and the luminance is controlled for each of the peripheral blocks adjacent to the outer periphery of the display screen. Accordingly, the luminance can be controlled more finely, thereby making it possible to provide a display screen having no visually uncomfortable feeling by the viewer as well as to more reliably prevent the outer periphery of the display from being damaged.